Moving irrigation systems, such as conventional pivot move and lateral move systems, are known to incorporate conduit truss span assemblies and a plurality of drop tubes by which a corresponding number of sprayheads incorporating rotatable water distribution plates (also referred to as rotor plates or spinners), fixed spray plates, or bubbler devices are suspended so as to be located in close proximity to crops or other plants.
In this regard, there are currently in use modular sprayheads, also manufactured by the assignee of this invention, that include sprinkler bodies and rotary stream distributors (or rotor plates) supported in cap assemblies that are designed for quick assembly and disassembly from the respective sprinkler bodies. The cap is typically secured to the sprinkler body by a conventional screw thread arrangement in combination with a locking mechanism where a plurality of vertically extending projections on the cap engage a corresponding plurality of notches formed on the cap mounting ring when the cap reaches the full extent of its rotational movement relative to the body during threading.
Rotor plates or spinners typically are fixed to a shaft that is, in turn, mounted within a housing in the sprinkler cap assembly. A rubber (or other suitable material) shaft seal is received over the shaft and held by means of a retainer on a support secured within a shaft housing on the cap. The retainer, however, leaves the sealing edge or lip of the shaft seal exposed. This arrangement can lead to damage to the seal through exposure to the elements, and may also hinder rotation of the shaft if debris migrates past the exposed lip of the seal.